1. Field of the Invention
This invention relates to memory modules, and more particularly, to a repairable memory module, such as a DRAM (dynamic random access memory) module, and a method of repairing such memory modules.
2. Description of Related Art
FIG. 1 is a schematic diagram of a conventional DRAM module which is designed for use with a 32-bit Pentium microprocessor on a personal computer. The DRAM module includes an array of eight 1M.times.4 DRAM ICs which are used together to constitute a 1M.times.32 SIMM (Single In-line Memory Module).
FIG. 2 shows a schematic top view of the conventional DRAM module of FIG. 1 when assembled. As shown, the DRAM module is formed by mounting eight DRAM ICs U1-U8 on a printed circuit board (PCB). The I/O (input/output) pins on these DRAM ICs are connected to corresponding I/O pins of the DRAM module.
Most conventional memory modules, as DRAM or flash memory modules, are manufactured by first arranging them in packaged form on a PCB and then separating them from the PCB so that they can serve as individual memory modules. These memory modules are then tested respectively through the so-called module testing process to check for any failed memory ICs in the module. If any memory IC is found to be failed, a conventional method for repairing the failed IC is simply to dismount the failed IC and then replaced it with a new, good one. This repair work, however, is quite laborious to carry out.
FIG. 3 is a flow diagram showing the procedural steps involved in a conventional module testing process to check for any failed ICs in the modules. As shown, if a memory module is OK, it is then ready for shipment to the customer; otherwise, the failed memory IC in the memory module is dismounted and then replaced with a new, good one. These two steps are collectively referred to a rework process, which is usually quite laborious and thus cost-ineffective to carry out.
A conventional method for manufacturing low-cost memory modules is to use the so-called chip-on-board (COB) technique. However, in a memory module based on the COB structure, the repair work for the failed ICs is difficult to carry out even before encapsulation is applied. After encapsulation, the repair work would be extremely difficult to carry out.